1. Field of the Invention
The present invention relates to pharmacologically active formulations and their method of use as kinase inhibitors.
2. Description of the Prior Art
Chronic Myelogenous Leukemia (CML) is the most common leukemia in adults. In 2014, an estimated 5,980 new cases of chronic myeloid leukemia (CML) are expected to be diagnosed and 810 deaths due to CML in the US. CML is a disease of hematopoietic stem cells and is characterized by the presence of a Philadelphia chromosome, a fusion of the Abelson murine leukemia (Abl) gene on chromosome 9 with the breakpoint cluster region (Bcr) gene on chromosome 22. This chimeric chromosome generates the Bcr-Abl gene. The resultant oncoprotein is a tyrosine kinase which interacts with a variety of signaling proteins such as RAS, RAF, JUN kinase, MYC and STAT, that lead to cellular transformation or that are involved in signaling pathways implicated in cellular transformation or cancer cell development.
Previously, drug therapy for CML was limited to nonspecific agents such as busulfan, hydroxyurea, and interferon-alpha (INF-a). INF-a led to regression of the disease and improved survival but was hindered by a multitude of toxicities. Allogeneic stem cell transplantation (SCT) was a curative intervention but carried a high risk of morbidity and mortality. Further, SCT is only an option for patients with excellent performance status and an appropriate stem cell donor.
Small molecule tyrosine kinase inhibitors (TKIs) were developed to exploit the presence of the aberrantly expressed Bcr-Abl protein in CML cells. Presently, there are four commercially available TKIs for the treatment of CML; these include imatinib, dasatinib, nilotinib, and ponatinib. Imatinib mesylate (Gleevec or Glivec as it is known in Europe) was the first TKI to receive approval by the Food and Drug Administration (FDA) for the treatment of patients with CML. It acts via competitive inhibition at the ATP-binding site of the Bcr-Abl protein, which results in the inhibition of phosphorylation of Bcr-Abl involved in cell signal transduction.
Phosphorylation of Bcr-Abl activates this enzyme and induces downstream signaling which promotes cell proliferation. Activation of Bcr-Abl results in the phosphorylation of one of its key targets, STAT5, a transcription factor involved in leukemogenesis. Phosphorylated STAT5 acts as a docking site for the SH2 domain of CrkL. CrkL and STAT5 then form a complex that translocates to the nucleus and induces transcription of genes involved in cell proliferation and cell survival. Fish E N, et al., “Activation of a CrkL-stat5 signaling complex by type I interferons,” The Journal of biological chemistry 1999, 274(2):571-573. Thus, STAT5 and CrkL are well established downstream targets of Bcr-Abl. Inhibition of Bcr-Abl with Gleevec (imatinib) reduces phosphorylation of both STAT5 and CrkL and attenuates their transcriptional activity. Capdeville R, et al., “Glivec (STI571, imatinib), a rationally developed, targeted anticancer drug,” Nature reviews Drug discovery 2002, 1(7):493-502. However, mutations acquired in the Bcr-Abl gene during CML progression were found to disable Gleevec activity which then failed to inhibit the CML progression. New drugs are needed to treat patients who have developed resistance to Gleevec.
This problem led to the rational development of second generation TKIs with hopes they would effectively treat patients unable to continue on Imatinib therapy. Dasatinib is an oral, second generation TKI that is 350 times more potent than Imatinib in vitro. In addition, it is also known to inhibit the Src family of kinases, which may also be critical in cell signaling pathways in CML. Inhibitors of Src kinases are also used in the treatment of CML.
Dasatinib was also able to induce more major molecular responses (MMR) compared to the imatinib group. Nilotinib is a structural analog of imatinib, though its affinity for the ATP binding site on Bcr-Abl is up to 50 times more potent in vitro. Like dasatinib, nilotinib initially demonstrated the ability to induce hematologic and cytogenetic responses in patients who had failed imatinib.
Commercially available drugs based on the TKIs mentioned previously show drug resistance due to the point mutations in the kinase domain of Bcr-Abl, which arrests the activity of the TKIs. Second generation TKIs are developed to overcome most of the mutations that confer resistance to imatinib, though novel mutations rendering the leukemia resistant to dasatinib and/or nilotinib have emerged. O'Hare T, et al., “Bcr-Abl kinase domain mutations, drug resistance, and the road to a cure for chronic myeloid leukemia,” Blood 2007, 110(7):2242-2249. One important mutation, the T315I, is known as the “gatekeeper” mutation, as it displays resistance to all currently available TKIs. Ponatinib, binds to the ATP binding pocket of the mutated Bcr-Abl and inhibits its activity. The FDA approved ponatinib for treatment of CML in 2012, but put a hold on its clinical use due to severe vascular toxicity. Since there were no other alternatives and due to desperate need for the treatment of Gleevec resistant CML patients, the FDA reapproved ponatinib in early 2014. Therefore, new therapies are needed to improve the outcome of this disease.